Electrical isolation of subterranean casing section

ABSTRACT

A method and apparatus for electrically-enhanced oil recovery from an oil-bearing subterranean formation are provided. An isolation opening extends around the circumference of a casing to provide a separation of the inflow section from an adjacent section of the casing. A portion of the oil-bearing formation disposed on the outside of the isolation opening is removed to form a void in the oil-bearing formation adjacent the isolation opening. A material having less electrical conductivity than the casing is inserted into the void and the isolation opening to form an insulative barrier.

PRIORITY CLAIM

The present application claims priority under §119 to U.S. Provisional Application No. 61/708,235 filed Oct. 1, 2012. The entire disclosure of the foregoing application is hereby incorporated herein by reference.

FIELD OF INVENTION

The present invention relates to a method for enhancing the production of oil from subterranean oil reservoirs. In particular, the present invention provides an improved system that uses an electric current passing through the oil reserves to enhance oil recovery.

BACKGROUND OF THE INVENTION

Recovery of heavy oil poses many challenges related to lack of oil mobility both in the formation and during artificial lift. Steam assisted gravity drainage is commonly used to improve or enable heavy oil production.

Methods for inducing electrical current into oil-bearing formations to improve recovery of oil reserves are described in U.S. Pat. Nos. 3,782,465, 4,495,990, 6,877,556, and 7,325,604, issued Feb. 5, 2008, the entire contents of which are incorporated herein by reference.

SUMMARY OF THE INVENTION

In light of the foregoing, the present invention addresses provides a method and apparatus for overcoming shortcomings of the prior art. To direct current flow through the oil bearing formation it is desirable to limit the extent of at least one electrode to the oil bearing formation. In accordance with one embodiment of this invention, this is accomplished by placing electrical isolating barriers projecting into the oil bearing formation from the casing at the top and the bottom of oil bearing formation. If the production casing does not extend past the bottom boundary of the oil bearing formation then only one isolating barrier is needed on top of the formation.

According to one aspect, the present invention provides a method for recovering oil from an oil-bearing subterranean formation employing a hollow well casing having an inflow section providing fluid flow from the oil-bearing formation into the casing. The method includes the step of providing an isolation opening extending around the circumference of the casing to provide a separation of the inflow section from an adjacent section of the casing. A portion of the oil-bearing formation disposed on the outside of the isolation opening is removed to form a void in the oil-bearing formation adjacent the isolation opening. A material having less electrical conductivity than the casing is inserted into the void and the isolation opening to form an insulative barrier.

According to another aspect, the present invention also provides a recovery apparatus for extracting oil using electrical enhanced oil recovery from an oil-bearing formation comprising a wellhead having a hollow casing with multiple sections extending through at least one non-oil-bearing formation into the oil bearing formation. The casing has an inflow section with at least one inflow opening in registry with the oil-bearing formation for extracting oil using electrically enhanced oil recovery. The inflow section is separated from an adjacent one of said multiple sections by a ring-shaped opening extending about the full 360 degree circumference of the casing, and an isolation barrier mounted in the ring-shaped opening. The barrier is comprises electrically non-conductive material isolating the inflow section from the adjacent section. The barrier has an interior dimension similar to the interior dimension of the casing sections on both sides of the barrier, and an exterior dimension extending beyond the exterior circumference of the casing sections and into the formation surrounding the ring-shaped opening between said adjacent casings sections.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an oil-field casing modified in accordance with the present invention to provide isolating barriers; within the oil-bearing formation;

FIG. 2 is a diagrammatic view (not to scale) of the oil-field casing of FIG. 1, showing the current flow from the perforated or slotted inflow section of the casing when used with a remote surface electrode;

FIG. 3 is a diagrammatic view (not to scale) of the oil-field casing of FIG. 1, showing the current flow from the perforated or slotted inflow section of the casing when used with a two-section casing, having isolated upper and lower casing sections above and below the perforated or slotted inflow section which serve as remote electrodes;

FIG. 4 is a diagrammatic view similar to FIG. 2 (not to scale), showing the casing terminating at its lower end in a lateral extension;

FIG. 5 is a perspective view of an isolating barrier; with a portion broken away;

FIG. 6 is a vertical sectional view of an isolating barrier insulated from the center of the casing by a layer of insulation; and

FIG. 7 is an enlarged fragmentary perspective view showing the components of the isolating barrier when the invention is used in a bore hole filled with conductive fluids.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIG. 1 a system for recovering subterranean oil reserves is illustrated. The system includes a well 10 extending into an oil-bearing formation 46. A production casing 44 extending into the well 10 has a perforated inflow section 45 adjacent the oil-bearing formation that allows fluid flow from the subterranean formations into the casing. A power source 20 is operable to induce an electrical current into the oil-bearing formation and a pump 41 b pumps oil and other fluids from the casing up to the surface through production tubing 41 a.

The details of the well structure will now be described in greater detail. The well 10 extends through subterranean layers 47 over the oil-bearing formation 46 and may extend into subterranean layers below the oil bearing formation, referred to as underburden. The production casing 44 is an axially elongated conduit extending into the well. The casing may be comprised of any of variety of materials, including, but not limited to electrically-conductive materials, such as metal. In the present instance, the production casing is formed of steel.

The production casing 44 is in fluid communication with a wellhead 41 from which the production casing hangs. An intermediate casing 13 surrounding the production casing extends into the overburden 47 and may be retained in place by a cement sheath surrounding the intermediate casing. A surface casing 12 extending into the ground adjacent the wellhead 41 surrounds the intermediate casing 13. The surface casing may be retained in place by a cement sheath surrounding the surface casing.

A perforated inflow section 45 in the casing 44 allows fluid to flow into the casing 45 from the surrounding oil-bearing formation. The perforations extend around the circumference of the casing and may be any of a variety of perforations, such as variously-shaped holes or slots, such as longitudinally-extending slots.

A pump 41 b within the casing 44 is operable to pump oil and/or other fluids through the casing 44 and/or out of the well 10. In particular, an elongated conduit, referred to as production tubing, may extend into the production casing 44 so that the bottom edge of the production tubing is positioned adjacent the perforated inflow section 45. The pump 41 b may be in fluid communication with the production tubing 41 a so that the pump 41 b pumps fluid from the casing up to the surface through the production tubing. In this way, the pump 41 b may be positioned adjacent the inflow section 45 of the casing 44.

The system further includes a power source 20 for inducing an electrical current into the subterranean layers and in particular into the oil-bearing layer 46. By inducing an electrical current into the oil bearing formation 46, which enhances oil production. For instance, the electrical current induced into the oil may provide one or more of the following affects on the fluid in the oil-bearing formation: reduction of oil viscosity due to temperature rise resulting from passage of electrical current; electro-kinetic processes, and/or electrochemical reactions that affect the properties of fluid and the medium matrix.

The power source 20 may provide an AC or DC current and is connected to two electrically conductive elements that operate as electrodes. For instance, the production casing 44 may be formed of metal and may be connected with the power source so that the production casing operates as one of the electrodes. The second electrode is located remotely from the casing so that the oil-bearing formation 46 is between the two electrodes. For instance, the second electrode may be a metallic plate or other conductive structure positioned at the surface or the casing of an adjacent well may be formed of electrically conductive material, such as metal, so that the adjacent well casing operates as the second electrode. Regardless of whether the second electrode is on the surface or subsurface, both electrodes are connected to the power source 20 to provide a current flow between the two electrodes.

In some applications, if the production casing 44 of a well 10 is used as an electrode, the induced current from the power source 20 may not pass through the oil in the oil-bearing formation 46 for a variety of reasons. One issue that may arise is due to the differing resistivities of the subterranean layers that cause only a small portion of the current to flow through the oil-bearing formation. Specifically, the majority of the induced current may bypass the oil-bearing formation 46, due to higher electrical conductivity in the overburden and underburden 47 surrounding the oil-bearing formations. Additionally, the surface area of the electrode in contact with the oil-bearing formation 46 is substantially smaller than that in contact with the rest of the formation, which can lead to only a small portion of the induced current passing through the oil in the oil-bearing formation.

To improve the current flow through the oil-bearing formation, the system includes one or more electrically-insulative barriers 49 along the length of the production casing 44. The barrier 49 operates to substantially isolate electrically one portion of the production casing from other portion or portions of the casing. For instance, as shown in FIG. 1, the power source 20 is connected with the inflow section 45 of the production casing 44. The barriers 49 substantially isolate the inflow section 45 electrically from the rest of the production casing. Accordingly, the induced current will tend to flow through the oil-bearing formation rather than along the production casing 44.

The barrier 49 is a radially extending structure that protrudes into the subterranean layers. Specifically, in the present instance, an upper barrier extends radially outwardly from the casing 44 adjacent the upper portion of the oil-bearing formation 46. If the production casing 44 extends through the oil-bearing formation, a lower barrier 49 may also be utilized. For instance, as shown in FIG. 1, a second barrier extends radially outwardly into the lower portion of the oil-bearing formation. In this way, a portion of the casing 44 operating as an electrode is electrically isolated from another portion of the casing, and in particular, is isolated from the portion of the casing above and below the barriers 49.

Although the barrier 49 has been described above as an element formed of an insulative material, it should be understood that the barrier may be configured in other manners that electrically isolate the portion of the casing 44 acting as the electrode from the rest of the casing. Specifically, a short length of the casing could be removed from between the electrode portion of the casing and the reset of the casing. For instance, the casing could be severed around the entire circumference of the casing so a gap is formed between the inflow portion 45 of the casing and the portion of the casing above the inflow portion. In this way, there is a break in the conductive path of the casing between the inflow portion 45 and the upper portion of the casing. Similarly, a section of the casing can be removed from the casing adjacent the lower portion of the oil-bearing formation 46.

Although the barriers 49 may be configured so that they are installed when the production casing 44 is installed into the well, in the typical scenario, the barriers 49 are installed after the casing 44 is already installed in the well 10. For instance, referring to FIGS. 1 and 5-6, a short section of the production casing may be cut-out. In the present instance, a section of the production casing approximately one foot long or less is severed from the production casing so that the production casing is not a continuous length of conduit. The casing 44 may be severed using any of a variety of techniques, such as milling, explosive cutting, jet milling, and/or chemical dissolution of the area of the casing where the opening or window is desired.

After severing the casing across the entire cross-section of the casing, the subterranean formation adjacent the severed section is also cut away to form a void or cavity 52 extending around the circumference of the production casing adjacent the opening. The cavity 52 extends radially outwardly into the subterranean layer, which in the present instance is the oil-bearing formation 46. For instance, the cavity may extend approximately 10-20 inches away from the casing. The cavity 52 also extends axially along the length of the casing 44 so that the length of the cavity along the length of the casing is longer than the length of casing that is severed from the casing.

After the casing is severed and the cavity is formed, non-conductive material is inserted into the cavity 52 and into the window formed in the casing 44. Any of a variety of non-conductive materials can be used to fill the cavity to form the barrier element. In the present instance, the non-conductive material is a readily deformable material, such as a liquid or generally flowable viscous material that is injected into the cavity 52 and into the window in the casing. If the non-conductive material is fluid or a generally flowable material, preferably the material is curable so that the material forms a generally rigid or stable structure in the form of the barrier 49. Although the non-conductive material can be any of a variety of generally insulative materials, such as plastic or rubber, in the present instance the material is an insulative epoxy injected into the cavity that cures to form a generally solid structure that electrically isolates and/or insulates the portion of the casing between the barriers 49 from the rest of the casing 44. When installing barriers both above and below the oil-bearing formation, the first barrier is allowed to set and solidify, before the second circumferential opening is made in the casing, so that the casing section between the barriers is stabilized while the second opening is being formed.

When the borehole will contain electrically conductive fluids, the fluid in the casing may provide an electrical pathway that will dissipate the electric flow from the power source. For instance, one of the fluids in the well may be salt water that may provide a conductive path. Therefore, an interior barrier may be provided to impede the induced current from traveling through the salt water along the length of the casing rather than through the oil-bearing formation. The interior barrier insulates the interior of the borehole, especially in the areas of the isolating barriers 49. FIGS. 6 and 7 illustrate an isolating barrier 52 between adjacent sections 44 a and 44 b of the casing 44. An insulating liner 55 covers the interior surface of the barrier 52. The liner 55 has a plurality of longitudinal passages 56 extending along its length to allow fluids to travel past the barrier. The passages 56 are closed by a fiberglass mandrel 57 within the liner 55. The closed passages may serve as conduits for use during the formation of the isolating barrier 52.

Referring now to FIG. 2, an alternate installation is illustrated in which a well casing 120 is used in conjunction with a surface electrode 121 and a power supply 122. The well casing 120 has an inflow section with perforations or slots forming an inflow section similar to the installation illustrated in FIG. 1. The inflow section in FIG. 2 is positioned in the oil-bearing formation 146 which falls between the adjoining overburden and underburden 147. The current flow is indicated by arrows 123.

Another alternate installation is illustrated in FIG. 3 in which a well casing 149 is separated into an upper section 149 a, and a lower section 149 c by a perforated or slotted inflow section 149 b. Isolating barriers 159 a and 159 b are mounted above and below the inflow section 149 b having perforations or slots to electrically isolate the inflow section 149 b from the upper and lower sections 149 a and 149 c. A power supply 152 has one side 150 connected to the inflow section and the other side connected to the upper and lower sections. The current flow generated by the power supply 152 is indicated by the arrows 153.

FIG. 4 shows an installation where a well casing 160 is used in conjunction with a surface electrode 161 and a power supply 162. The well casing 160 terminates in a lateral extension having a first section 169 a, a perforated or slotted inflow section 169 b, and a terminal section 169 c in the oil-bearing formation 166 which falls between the adjoining overburden and underburden 147. The inflow section 169 b is isolated from the sections 169 a and 169 c by isolating barriers 179 a and 179 b. The current flow is indicated by arrows 163.

In the embodiments illustrated in FIGS. 2 and 3, two electrical isolating barriers 159 a and 159 b are positioned about the perimeter of the casing on opposite sides of the inflow section, so as to divert the electric current flow in either direction. However if the casing terminates beyond the inflow section within the oil-bearing formation, the second barrier 159 b may be omitted.

While particular embodiments of the invention have been illustrated and described, changes or modifications may be made without departing from the inventive concepts as set forth in the following claims: 

1. In a recovery apparatus employing electrical enhanced oil recovery from an oil-bearing formation, the apparatus comprising a wellhead having a hollow casing extending through at least one non-oil-bearing formation into the oil bearing formation, the casing having an inflow section with at least one inflow opening into the oil-bearing formation for extracting oil using electrically enhanced oil recovery, the method for improving the efficiency of the extracting by forming an electrical isolation barrier within the oil-bearing layer adjacent the inflow opening of casing, comprising the steps of providing an isolation opening extending around the circumference of the casing to provide a separation of the inflow section from an adjacent section of the casing, removing a portion of the formation disposed on the outside of the isolation opening to form a void in the oil-forming formation, providing a quantity of material into the void and the isolation opening to form an insulative barrier.
 2. The method of claim 1 including the steps of providing a second isolation opening extending around the circumference of the casing on the opposite side of the inflow opening to provide access between the formation outside the casing and the interior of the casing, removing a portion of the formation disposed on the outside of the isolation opening to form a second void in said formation, providing a quantity of insulative material sufficient to fill said second void and the second isolation opening and filling said second void and said isolation opening with said flowable material, and treating the flowable material to solidify the flowable material contained within the second void and the second isolation opening to form a second isolation barrier.
 3. The method of claim 1 wherein said isolation barrier and said adjacent casing sections have interior surfaces, including the further step of shaping the interior surface of said isolation barrier to conform to the interior surfaces of the adjacent casing sections.
 4. The method of claim 1 including the further step of providing a hollow cylindrical insulating liner formed of an electrical insulation material, and applying the liner over the inward surface of said isolation barrier.
 5. The method of claim 1 including the further steps of providing passages on the inner surface of said liner, and closing the passages by a mandrel positioned within the inner surface.
 6. The method clam 1, wherein the casing comprises multiple sections, each having a hollow cylindrical shell of an electrically conductive material, wherein the step of providing an isolation opening is performed by removing a 360 degree ring of the conductive material of the hollow cylindrical shell.
 7. The method of claim 6 wherein said step of removing a 360 degree ring is performed by cutting away the electrically conductive material.
 8. The method of claim 6 wherein the step of removing a 360 degree ring is performed by applying a chemical material to the ring to dissolve the same.
 9. In a recovery apparatus employing electrical enhanced oil recovery from an oil-bearing formation, the apparatus comprising a wellhead having a hollow casing extending through at least one non-oil-bearing formation, the casing having an inflow section with at least one inflow opening into the oil-bearing formation for extracting oil using electrically enhanced oil recovery, the method for improving the efficiency of the extracting by forming electrical isolation barriers within the oil-bearing layer on opposite sides of the inflow opening of the casing, comprising the steps of forming isolation openings extending substantially 360 degrees about the circumference of the casing on opposite sides of said inflow openings to provide access between the oil-bearing formation and the interior of the casing, removing a portion of the oil-bearing formation disposed on the outside of each opening of said casing to form voids in said formation, providing a quantity of flowable material sufficient to fill said voids and said isolation openings and injecting said material into said voids and said isolation openings, and treating said flowable material to solidify said flowable material contained within said voids and said isolation openings to form isolation barriers interrupting electrical communication between the inflow section and the reminder of said casing.
 10. Recovery apparatus for extracting oil using electrical enhanced oil recovery from an oil-bearing formation comprising a wellhead having a hollow casing with multiple sections extending through at least one non-oil-bearing formation into the oil bearing formation, the casing having an inflow section with at least one inflow opening in registry with the oil-bearing formation for extracting oil using electrically enhanced oil recovery, said inflow section being separated from an adjacent one of said multiple sections by a ring-shaped opening extending around the circumference of the casing, and an isolation barrier mounted in said ring-shaped opening to maintain the physical continuity of the casing and operable to improve the efficiency of the extracting, the barrier comprising electrically non-conductive material isolating said inflow section from the adjacent section, the barrier having an interior dimension substantially similar to the interior dimension of the casing sections on both sides of the barrier, and an exterior dimension extending beyond the exterior circumference of said casing sections and into the formation surrounding said ring-shaped opening between said adjacent casings sections.
 11. Recovery apparatus according to claim 10 wherein said isolation barrier material has flowable state when it is first inserted into said ring-shaped opening and into the formation surrounding said opening, and is curable into a solid state when the insertion is complete. 